to cap or not to cap, that is the question...

I have 2 8" RF Punch XLC runnign right now off a hifonics Zeus z400 amp, 2 ohms, etc, they hit liek mudda for 8's lol i love em, unfortunately, with only these 2 running and no otehr amp, my lights dim when idling, and the interior lights dim occasionally when driving, not the headlights tho.
1991 Mercury cougar LS, with teh 302 5.0L V8.
The worst part is, I'm about to get hte alpne type R components, and likely an amp for them.
Oh wait, i forgot what was turly the worst part lol. My 12" RF Punch Power DVC is jsut sitting in the triple box, with no power running to it yet! I DO want to hook it up, but i am definitely ahving some power issues here lol, the plan is a JBL 1200.1 or a JBL600.1, depending on the cash flow issue.
Should I cap, get a new alternator? what should i do?! I need help! lol.